The present invention relates to a medical electrode to be used for delivering electrical energy to a living body as in the case of a dual-use electrode for use in, e.g., defibrillation and pacing. The present invention also relates to a medical electrode to be used both for delivering a large amount of electrical energy to a living body and for detecting an electrical potential of the living body as in the case of an electrode for use both in, e.g., defibrillation and detection of an electrocardiogram signal.
A conductive layer of the medical electrode is usually formed from a metal plate comprising tin as the main ingredient. In order to reduce impedance existing between the metal plate and the skin of the living body, a conductive gel layer is interposed therebetween. However, in the case of a medical electrode delivered with a large amount of electrical energy, as in the case of an electrode for defibrillation purpose, the conductive gel is subjected to electrolysis, and thus evolves a hydrogen gas and a chlorine gas. These gases collect between the metal plate and the gel layer, causing a change in an electrical characteristic of the electrode or corrosion of the metal plate. Moreover, corrosion of the metal plate, which is induced by an electrolyte (salt) contained in the gel, also arises, which in turn causes a failure.
Japanese Patent Publication No. 10-507651A discloses an electrode comprising a breathable conductive layer, and a gas affinity layer superposed on the conductive layer (cf., pages 7–19 and FIGS. 1–5). As a result, the gas developed in the gel layer passes through the conductive layer and escapes to the outside by way of the gas affinity layer.
However, an electrode using a metal plate as a conductive layer suffers a drawback of corrosion of the conductive layer decreasing in conductivity. Meanwhile, the electrode using carbon for a conductive layer is less apt to corrode and has little chance of decreasing in conductivity. However, restoration of a potential is slow after application of a large defibrillation current, and the electrode suffers a drawback of consumption of much time before the electrode can be used for detecting an electrocardiogram signal.
Standards for a defibrillation electrode include a drop in an electric potential between electrodes to a predetermined voltage level or less within a predetermined period of time after delivery of defibrillation electrical energy.